aria2 - The ultra fast download utility

1. Disclaimer
-------------
This program comes with no warranty.
You must use this program at your own risk.

2. About aria2
--------------
aria2 has segmented downloading engine in its core. By segmented downloading,
it can download files very much faster than ordinary browsers.

aria2 is in very early development stage. Currently it has following features:
* HTTP/HTTPS GET support
* HTTP Proxy support
* HTTP BASIC authentication support
* HTTP Proxy authentication support
* FTP support(active, passive mode)
* FTP through HTTP proxy(GET command or tunneling)
* Segmented download
* Cookie support
* It can load cookies from file whose format is used by Netscape and Mozilla.
* It can run as a daemon process.
* BitTorrent protocol support with fast extension.
* Selective download in multi-file torrent/metalink.
* Metalink version 3.0 support(HTTP/FTP/BitTorrent).
* Limits download/upload speed.
* Chunk checksum validation in Metalink.
* netrc support.
* Configuration file support.
* Downloads URIs found in a text file or stdin.
* Integrates HTTP/FTP/BitTorrent downloads; downloading a file from several
  different sources.

3. Dependency
-------------
In order to enable HTTPS support, you need GNU TLS or OpenSSL.
In order to enable BitTorrent support, you need GNU TLS+libgcrypt or OpenSSL.
In order to enable Metalink support, you need libxml2 or Expat. Optionally
GNU TLS+libgcrypt or OpenSSL are required for checksum checking support(MD5,
SHA1, SHA256).

Note;;
  GNU TLS has precedence over OpenSSL if both libraries are installed.
  If you prefer OpenSSL, run configure with "--without-gnutls".

Note;;
  libxml2 has precedence over Expat if both libraries are installed.
  If you prefer Expat, run configure with "--without-libxml2".

You can disable BitTorrent, Metalink support by providing --disable-bittorrent,
--disable-metalink respectively to configure script.

In order to enable async DNS support, you need c-ares or ares.
c-ares: http://daniel.haxx.se/projects/c-ares/
ares: ftp://athena-dist.mit.edu/pub/ATHENA/ares

4. How to build
---------------
In order to build aria2 from the source package, you need following development
packages(package name may vary depending on the distribution you use):

* libgnutls-dev    (Required for HTTPS, BitTorrent support)
* libgpg-error-dev (Required for BitTorrent support)
* libgcrypt-dev    (Required for BitTorrent support)
* libares-dev      (Required for async DNS support)
* libxml2-dev      (Required for Metalink support)

You can use libssl-dev instead of libgnutls-dev,libgpg-error-dev,libgcrypt-dev:
* libssl-dev       (Required for HTTPS, BitTorrent support)

You can use libexpat1-dev instead of libxml2-dev:
* libexpat1-dev    (Required for Metalink support)

The build process is fairly standard way for *nix programs:

$ ./configure
$ make

The executable is aria2c in src directory.

5. BitTorrrent
--------------
The filename of the downloaded file is determined as follows:

single-file mode:
    If "name" key is present in .torrent file, filename is the value of "name"
    key. Otherwise, filename is the basename of .torrent file appended by
    ".file". For example, .torrent file is "test.torrrent", then filename is
    "test.torrent.file".
    The directory to store the downloaded file can be specified by -d option.
multi-file mode:
    The complete directory/file structure mentioned in .torrent file is
    created.
    The directory to store the top directory of downloaded files can be
    specified by -d option.

In the default behavior, before download starts, complete directory structure
is created if needed. Then aria2 opens all files mentioned in .torrent file,
directly writes to and reads from these files.
NOTE: Even in selective download, all files are opened.

If "--direct-file-mapping" option set to be false, aria2 creates temporary
file in the store directory. The length of this file is the sum of length of
the files in .torrent file, so at least 2 times more disk space than the file
size itself is required. Writing and reading is done against this file.
After download completes, aria2 creates complete directory structure if needed,
and copies whole file or a part of it to the destination.

Note:
*  -o option is used to change the filename of downloaded .torrent file.
* The ports aria2c uses are 6881-6999.
* The maximum number of peers is 55. This limit may be exceeded when download
rate is low.
* As of release 0.10.0, aria2 stops sending request message after selective
  download completes,

6. Metalink
-----------
The current implementation supports HTTP/FTP/BitTorrent.
The other P2P protocols are ignored.

For checksum checking, MD5, SHA1, SHA256 are supported. If multiple hash
algorithms are provided, aria2 uses SHA1. If checksum checking is failed, aria2
doesn't retry the download and just exits with non-zero return code.

The supported user preferences are version, language, location, protocol and
os.

If chunk checksums are provided in Metalink file, aria2 automatically validate
a chunk of file while downloading it. This behavior can be turned off by
a command-line option.

7. netrc
--------
netrc support is enabled by default in ftp.
To disable netrc support, specify -n command-line option.
Your .netrc file should have correct permissions(600).

8. Configuration file
---------------------
Configuration file must be placed under ~/.aria2 and must be named as aria2.conf.
In each line, there is 1 parameter whose syntax is name=value pair,
where name is the long command-line option name without '--' prefix.
The lines beginning '#' are treated as comments.

Example:

# sample configuration file for aria2c
file-allocation=prealloc
listen-port=60000
seed-ratio=1.0
max-upload-limit=40K
ftp-pasv=true